Direct searches for Dark Matter particles

Transcription

1 P. Belli INFN-Roma Tor Vergata TAUP 2007, Sendai, September 2007 Direct searches for Dark Matter particles (above LN 2 temperature)

2 Relic DM particles from primordial Universe Heavy candidates: In thermal equilibrium in the early stage of Universe Non relativistic at decoupling time: <σ ann. v> ~ /Ω WIMP h 2 cm 3 s -1 σ ordinary matter ~ σ weak Expected flux: Φ ~ (GeV/m W ) cm -2 s -1 (0.2<ρ halo <1.7 GeV cm -3 ) Form a dissipationless gas trapped in the gravitational field of the Galaxy (v ~10-3 c) Neutral, massive, stable (or with half life ~ age of Universe) and weakly interacting Light candidates: axion, sterile neutrino, axionlike particles cold or warm DM (no positive results from direct searches for relic axions with resonant cavity) SUSY (R-parity conserved LSP is stable) neutralino or sneutrino the sneutrino in the Smith and Weiner scenario sterile ν axion-like (light pseudoscalar and scalar candidate) self-interacting dark matter mirror dark matter Kaluza-Klein particles (LKK) electron interacting dark matter a heavy ν of the 4-th family + multi-component halo? even a suitable particle not yet foreseen by theories etc heavy exotic canditates, as 4th family atoms,...

3 What accelerators can do: to demostrate the existence of some of the possible DM candidates What accelerators cannot do: to credit that a certain particle is the Dark Matter solution or the single Dark Matter particle solution + DM candidates and scenarios exist (even for neutralino candidate) on which accelerators cannot give any information DM direct detection method using a model independent approach

4 Some direct detection processes: DMp Ionization: Ge, Si Scatterings on nuclei detection of nuclear recoil energy DMp N Bolometer: TeO 2, Ge, CaWO 4,... Scintillation: NaI(Tl), LXe,CaF 2 (Eu), Excitation of bound electrons in scatterings on nuclei detection of recoil nuclei + e.m. radiation Conversion of particle into electromagnetic radiation detection of γ, X-rays, e - Interaction only on atomic electrons detection of e.m. radiation a X-ray DMp γ e - e - e.g. signals from these candidates are completely lost in experiments based on rejection procedures of the electromagnetic component of their counting rate and more

5 Dark Matter direct detection activities in underground labs Various approaches and techniques (many still at R&D stage) Various different target materials Various different experimental site depths Different radiopurity levels, etc. Gran Sasso (depth ~ 3600 m.w.e.): DAMA/NaI, DAMA/LIBRA, DAMA/LXe, HDMS, WARP, CRESST, Xenon10 Boulby (depth ~ 3000 m.w.e.): Drift, Zeplin, NAIAD Modane (depth ~ 4800 m.w.e.): Edelweiss Canfranc (depth ~ 2500 m.w.e.): ANAIS, Rosebud, ArDM Snolab (depth ~ 6000 m.w.e.): Picasso, DEAP, CLEAN Stanford (depth ~10 m): CDMS I Soudan (depth ~ 2000 m.w.e.): CDMS II Y2L (depth ~ 700 m): KIMS Oto (depth ~ 1400 m.w.e.): PICO-LON Kamioka (depth ~2700 m.w.e.): XMASS

6 DIRECT DETECTION EXPERIMENTS Experiment Target Type Status Site ANAIS NaI annual modulation construction Canfranc DAMA/NaI NaI annual modulation concluded LNGS DAMA/LIBRA NaI annual modulation running LNGS DAMA/1 ton NaI annual modulation R&D LNGS NAIAD NaI PSD concluded Boulby HDMS Ge ionization concluded LNGS KIMS CsI PSD R&D Y2L (Korea) Caf 2 -Kamioka CaF 2 PSD running Kamioka DAMA/LXe LXe PSD running LNGS WARP LAr 2 phase running LNGS XENON 10 LXe 2 phase running LNGS Zeplin II LXe 2 phase running Boulby Zeplin III LXe 2 phase installation Boulby ArDM LAr 2 phase R&D Canfranc LUX LXe 2 phase R&D Dusel CLEAN LNe PSD R&D DEAP LAr PSD R&D SNOLAB XMASS LXe PSD construction Kamioka CDMS Ge bolometer running Soudan CRESST CaWO 4 bolometer running LNGS EDELWEISS Ge bolometer running Frejus ROSEBUD Ge, sap,tung bolometer R&D Canfranc COUPP F SH droplet R&D PICASSO F SH droplet running + R&D SNOLAB SIMPLE F SH droplet running + R&D Bas Bruit Drift CS 2 gas TPC R&D Boulby MIMAC 3 He gas TPC R&D

7 Experiments using liquid noble gases Single phase: LXe,LAr, LNe scintillation, ionization Dual phase liquid /gas scintillation + scintillation Background rejection in single phase detector: pulse shape discrimination γ/recoils from the UV scintillation photons in dual phase detector: prompt signal (S1): UV photons from excitation and ionisation delayed signal (S2): e - drifted into gas phase and secondary scintillation due to ionization in electric field DAMA/LXe ZEPLIN-I DAMA/LXe: low background developments and applications to dark matter investigation (since N.Cim. A 103 (1990) 767) XENON10, WARP, ZEPLIN-II

8 Recent results of a liquid noble gas experiment: XENON10 (arxiv: ) Experimental site: Target material: Target mass: Used exposure: Gran Sasso (1400 m depth) nat Xe 5.4 kg (tot: 15 kg) 136 kg day But cautious actitude: Many cuts are applied, each of them can introduce systematics. The systematics can be variable along the data taking period; can they and the related efficiencies be suitably evaluated in short period calibration? 50% efficiency Ten events survives the many cuts. Some speculations about their nature. Has the (intrinsic) limitations of the method been reached?

9 Recent results of a liquid noble gas experiment: WARP Experimental site: Gran Sasso (1400 m depth) Target material: Target volume: Used exposure: nat Ar 2.3 liters 96.5 kg day (arxiv: ) Integral Rate = cpd/kg But cautious actitude: Many cuts are applied, each of them can introduce systematics. The systematics can be variable along the data taking period; can they and the related efficiencies be suitably evaluated in short period calibration? Eight events survives the many cuts. Some speculations about their nature. Has the (intrinsic) limitations of the method been reached?

10 ZEPLIN-II II Experimental site: Detector: Exposure: Boulby mine 7.2 kg (tot: 31 kg) two phase Xenon 225 kg x day Discrimination between nuclear recoils and background electron recoils by recording scintillation and ionisation signals generated within the liquid xenon Cuts Many cuts are applied, each of them can introduce systematics. The systematics can be variable along the data taking period; can they and the related efficiencies be suitably evaluated in short period calibration? (astro-ph/ ) 50% efficiency Rn within active volume In the acceptance region registered 29 events Some speculations about their nature: interpreted as γ and radon progeny induced background Has the (intrinsic) limitations of the method been reached?

11 ... some warnings, comments,... on dual phase detectors Physical energy threshold unproved by source calibrations Disuniformity of detector: intrinsic limit? corrections applied: which systematics? The used gas is natural xenon and argon, that is with an unavoidable content of Kripton and 39 Ar, respectively Duty cycles Small light responses (e.g. 2.2 and ph.e./kevee for XENON10 and for WARP, respectively) Poor energy resolutions (e.g. σ/e 13% and 122 kev for WARP and ZEPLIN, respectively) Despite of the small light response an energy threshold of 2 kevee is claimed (XENON10) What about the energy resolution at 2 kev (XENON10)? It is quite hard to justify low levels of bckg taking into account all the materials involved in the core of the experiment. Case of XENON10: 89 PMTs (with photocathodes of Rb-Cs-Sb), all the materials for the electric field, the stainless steel containers,... WARP: for γ: 122 kev (they quote 2.9 ph.e./kev) for recoils: they quote Y Ar 1.6 ph.e./kev quenching factor for recoils: >0.6? Notwithstanding the larger A of Xenon than that of Germanium, much lower WIMP masses are reported as reached in sensitivity in an exclusion plot under the single set of used expt and theo assumptions. How is it robust? It depends on all the assumptions about the energy thresholds, energy resolutions,... How does the exclusion plot depend on the used parametrization for the energy resolution? for the light correction... + never universal boundary!

12 Examples of energy resolutions: comparison with NaI(Tl) NaI(Tl) astro-ph/ , Jan 2007 σ ( 60keV ) = 6.8% E 241 Am WARP WARP ZEPLIN-II arxiv:astro-ph/ v2 Co-57 XENON10 subtraction of the spectrum? XENON kev = 16%

13 Some other direct detection activities either in preparation or at R&D stage ArDM: ton scale dual-phase Argon detector WARP: double phase Argon detector at LNGS (fiducial volume 100 liters) CLEAN: Cryogenic Low Energy Astrophysics with Neon Single phase liquid Neon detector of tens of tons DEAP (SNOLAB): scintillation light in LAr at 85K PSD studying different lifetimes in singlet/ triplet states for electrons and nuclear recoil (ton scale) Lux: dual phase time projection chamber with 100 kg LXe (tot: 300 kg) SIGN: A High-Pressure, Room-Temperature, Gaseous-Neon-Based Underground Physics Detector ( atm towards 10 tons) they should certainly profit by the previous experience to suitably improve the detectors responses and performances

14 a discrimination on an eventby-event base is possible just for zero systematics. Rejection procedures would require a much deeper and quantitative investigation than those done up to now at very small scale (from grams to few kg) e.m. component of the rate can contain the signal or part of it even assuming pure recoil case and ideal discrimination on an event-byevent base, the result will NOT be the identification of the presence of WIMP elastic scatterings as DM signal, because of the well known existing recoil-like undistinguishable background Therefore, even in the ideal case the excellent background suppression can not provide a signal identification A model independent signature is needed Directionality Correlation of Dark Matter impinging direction with Earth's galactic motion due to the distribution of Dark Matter particles velocities very hard to realize Diurnal modulation Daily variation of the interaction rate due to different Earth depth crossed by the Dark Matter particles only for high σ 30 km/s December Annual modulation Annual variation of the interaction rate due to Earth motion around the Sun at present the only feasible one June 30 km/s ~ 232 km/s 60

15 DRIFT-IIa IIa Experimental site: Boulby mine Identification of the Dark Matter particle by exploiting the non-isotropic recoil distribution correlated to the Earth position with to the Sun de/dx discrimination between gammas and neutrons After an exposure of 10.2 kg x days a population of nuclear recoils (interpreted as due to the decay of unexpected 222 Rn daughter nuclei, present in the chamber) has been observed. Not yet results on Dark Matter particle

16 The annual modulation: a model independent signature for the investigation of Dark Matter particles component in the galactic halo With the present technology, the annual modulation is the main model independent signature for the DM signal. Although the modulation effect is expected to be relatively small a suitable large-mass, low-radioactive set-up with an efficient control of the running conditions would point out its presence. Drukier, Freese, Spergel PRD86 Freese et al. PRD88 30 km/s December v sun ~ 232 km/s (Sun velocity in the halo) v orb = 30 km/s (Earth velocity around the Sun) γ = π/3 ω = 2π/T T = 1 year t 0 = 2 nd June (when v is maximum) June 30 km/s ~ 232 km/s 60 Requirements of the annual modulation S k v (t) = v sun + v orb cosγcos[ω(t-t 0 )] dr [ η( t)] = der S0, k + Sm, k cos[ ω( t t0)] de E k R Expected rate in given energy bin changes because the annual motion of the Earth around the Sun moving in the Galaxy 1) Modulated rate according cosine 2) In a definite low energy range 3) With a proper period (1 year) 4) With proper phase (about 2 June) 5) For single hit events in a multi-detector set-up 6) With modulation amplitude in the region of maximal sensitivity must be <7% for usually adopted halo distributions, but it can be larger in case of some possible scenarios To mimic this signature, spurious effects and side reactions must not only - obviously - be able to account for the whole observed modulation amplitude, but also to satisfy contemporaneously all the requirements

17 Roma2,Roma1,LNGS,IHEP/Beijing DAMA/NaI DAMA/LIBRA DAMA/LXe DAMA/R&D low bckg DAMA/Ge for sampling meas.

18 DAMA/NaI(Tl)~100 kg Performances: N.Cim.A112(1999) , EPJC18(2000)283, Riv.N.Cim.26 n. 1(2003)1-73, IJMPD13(2004)2127 Results on rare processes: Possible Pauli exclusion principle violation CNC processes Electron stability and non-paulian transitions in Iodine atoms (by L-shell) Search for solar axions Exotic Matter search Search for superdense nuclear matter Search for heavy clusters decays PLB408(1997)439 PRC60(1999) PLB460(1999)235 PLB515(2001)6 EPJdirect C14(2002)1 EPJA23(2005)7 EPJA24(2005)51 Results on DM particles: PSD PLB389(1996)757 Investigation on diurnal effect N.Cim.A112(1999)1541 Exotic Dark Matter search PRL83(1999)4918 Annual Modulation Signature PLB424(1998)195, PLB450(1999)448, PRD61(1999)023512, PLB480(2000)23, EPJC18(2000)283, PLB509(2001)197, EPJC23(2002)61, PRD66(2002)043503, Riv.N.Cim.26 n.1 (2003)1-73, IJMPD13(2004)2127, IJMPA21(2006)1445, EPJC47(2006)263, IJMPA22(2007) other works in progress... total exposure collected in 7 annual cycles data taking completed on July 2002 (still producing results) kg d

19 The final model independent result by DAMA/NaI Experimental residual rate of the single hit events in 2-6 kev over 7 annual cycles 7 annual cycles: total exposure ~ 1.1 x 10 5 kg d Riv. N. Cim. 26 n. 1 (2003) 1-73, IJMPD 13 (2004) 2127 Power spectrum 2-6 kev experimental residual rate of the multiple hit events (DAMA/NaI-6 and 7) in the 2-6 kev energy interval: A = -(3.9±7.9) 10-4 cpd/kg/kev 6-14 kev 2-6 kev Acos[ω(t-t 0 )] Time (day) P(A=0) = Solid line: t 0 = days, T = 1.00 years from the fit: A = ( ± ) cpd/kg/kev from the fit with all the parameters free: A = ( ± ) cpd/kg/kev t 0 = (140 ± 22) d T = (1.00 ± 0.01) y No systematics or side reaction able to account for the measured modulation amplitude and to satisfy all the peculiarities of the signature Principal mode d -1 1 y -1 experimental residual rate of the single hit events (DAMA/NaI-1 to 7) in the 2-6 kev energy interval: A = (0.0195±0.0031) cpd/kg/kev Multiple hits events = Dark Matter particle switched off All the peculiarities of the signature satisfied This result offers an additional strong support for the presence of DM particles in the galactic halo further excluding any side effect either from hardware or from software procedures or from background model independent evidence of a particle Dark Matter component in the galactic halo at 6.3σ C.L.

20 Summary of the results obtained in the investigations of possible systematics or side reactions (see for details Riv. N. Cim. 26 n. 1 (2003) 1-73, IJMPD13(2004)2127 and references therein) Source Main comment Cautious upper limit (90%C.L.) RADON installation excluded by external Rn + 3 levels of sealing in HP Nitrogen atmosphere, etc TEMPERATURE Installation is air conditioned + detectors in Cu housings directly in contact with multi-ton shield huge heat capacity + T continuously recorded + etc. NOISE ENERGY SCALE <0.2% S m obs <0.5% S m obs Effective noise rejection near threshold (τ noise tens ns, τ NaI hundreds ns) <1% S m obs X-rays + periodical calibrations in the same running conditions + continuous monitoring of 210 Pb peak <1% S m obs EFFICIENCIES Regularly measured by dedicated calibrations <1% S m obs BACKGROUND No modulation observed above 6 kev + this limit includes possible effect of thermal and fast neutrons + no modulation observed in the multiple-hits events in 2-6 kev region <0.5% S m obs SIDE REACTIONS Muon flux variation measured by MACRO <0.3% S m obs + even if larger they cannot satisfy all the requirements of annual modulation signature Thus, they can not mimic the observed annual modulation effect

21 ... about the interpretation of the direct DM experimental results Presence of modulation for 7 annual cycles at ~6.3σ C.L. with the proper distinctive features of the signature; all the features satisfied by the data over 7 independent experiments of 1 year each one The positive and model independent result of DAMA/NaI Absence of known sources of possible systematics and side processes able to quantitatively account for the observed effect and to contemporaneously satisfy the many peculiarities of the signature No other experiment whose result can be directly compared in model independent way is available so far To investigate the nature and coupling with ordinary matter of the possible DM candidate(s), effective energy and time correlation analysis of the events has to be performed within given model frameworks Corollary quests for candidates astrophysical models: ρ DM, velocity distribution and its parameters nuclear and particle Physics models experimental parameters a model or a model e.g. for WIMP class particles: SI, SD, mixed SI&SD, preferred inelastic, scaling laws on cross sections, form factors and related parameters, spin factors, halo models, etc. + different scenarios + multi-component halo? THUS uncertainties on models and comparisons

22 First case: the case of DM particle scatterings on target-nuclei. When just the recoil energy is the detected quantity DMp DM particle-nucleus elastic scattering (SI, SD, SI&SD coupling) DMp N Preferred inelastic DM particle-nucleus scattering (S m /S 0 enhanced with respect to the elastic scattering case) The differential energy distribution depends: on the assumed scaling laws, nuclear form factors, spin factors, free parameters ( kind of coupling, mixed SI&SD, pure SI, pure SD, pure SD through Z 0 exchange, pure SD with dominant coupling on proton, pure SD with dominant coupling on neutron, preferred inelastic,...), on the assumed astrophysical model (halo model, presence of non-thermalized components, particle velocity distribution, particle density in the halo,...) on instrumental quantities (quenching factors, energy resolution, efficiency,...)

23 Few examples of corollary quests for the WIMP class - DAMA/NaI WIMP class: examples of allowed volumes/regions DM particle with elastic DM particle with dominant SI&SD interactions SI coupling in given scenarios (Riv. N. Cim. 26 n. 1 (2003) 1-73, IJMPD 13 (2004) 2127) DM particle with dominant SD coupling DM particle with preferred inelastic interaction Examples of slices of the allowed volume in the space (ξσ SI, ξσ SD, m W, θ) for some of the possible θ (tgθ =a n /a p with 0 θ<π) and m W Example of a slice (θ=π/4; 0 θ<π) of the allowed volume in the space (m W, ξσ SD,θ) Most of these allowed volumes/regions are unexplorable e.g. by Ge, Si, TeO 2, Ar, Xe, CaWO 4 targets not exhaustive + different scenarios? + different halo features? Example: Investigating the effect of Sagittarius Dwarf satellite galaxy (SagDEG) Possible contributions due to the tidal stream of Sagittarius Dwarf satellite (SagDEG) galaxy of Milky Way EPJC47(2006)263 few examples signature: SagDEG tail affects the phase of the annual modulation signal pure SI case green areas: no SagDEG pure SD case: examples of slices of the 3-dim allowed volume

24 Other contributions and effects involved in the DM particle scatterings on target-nuclei?

25 Investigating electromagnetic contributions in the detection of WIMP candidates Ionization and the excitation of bound atomic electrons induced by the presence of a recoiling atomic nucleus in the case of the WIMP-nucleus elastic scattering (named hereafter Migdal effect) The effect is well known since long time Example accounting for Migdal effect IJMPA 22 (2007) 3155 the recoiling nucleus can "shake off" some of the atomic electrons recoil signal + e.m. contribution made of the escaping electron, X-rays, Auger electrons arising from the rearrangement of the atomic shells e.m. radiation fully contained in a detector of suitable size Adopted assumptions in the examples: i) WIMP with dominant SI coupling and with σ A 2 ; ii) non-rotating Evans logarithmic galactic halo model with R c =5kpc, v 0 =170 km/s, ρ 0 = 0,42 GeV cm -3 iii) form factors and q of 23 Na and 127 I as in case C of Riv.N.Cim 26 n1 (2003)1 Example of a purely SI WIMP Although the effect of the inclusion of the Migdal effect appears quite small: - the unquenched nature of the e.m. contribution - the behaviour of the energy distribution for nuclear recoils induced by WIMP-nucleus elastic scatterings -etc. can give an appreciable impact at low WIMP masses Example of a purely SD WIMP WARNING: 1) to point out just the impact of the Migdal effect the SagDEG contribution has not been included here. 2) considered frameworks as in Riv.N.Cim 26 n1 (2003)1

26 Further uncertainties in the quest for WIMPs: the case of the recoils quenching In crystals, ions move in a different manner than that in amorphous materials. In the case of motion along crystallographic axes and planes, a channeling effect is possible, which is manifested in an anomalously deep penetration of ions into the target. Channeling effect in crystals Occurs in crystalline materials due to correlated collisions of ions with target atoms. Steering of the ions through the open channels can result in ranges several times the maximum range in no-steering directions or in amorphous materials. Electronic losses determine the range and there is very little straggling. ROM2F/2007/15, to appear arxiv: Well-known effect, discovered on 1957, when a deep penetration of 134 Cs + ions into a Ge crystal to a depth λ c 10 3 Å was measured (according to SRIM, a 4 kev Cs + ion would penetrate into amorphous Ge to a depth λ a = 44 Å, S n /S e = 32 and q=0.03). Within a channel, mostly electronic stopping takes place (in the given example, λ c λ a /q 1450 Å). When a low-energy ion goes into a channel, its energy losses are mainly due to the electronic contributions. This implies that a channeled ion transfers its energy mainly to electrons rather than to the nuclei in the lattice and, thus, its quenching factor approaches the unity. R ion ( E) R.( E) Lion L el el q( E) 1

27 Modeling the channeling effect: Examples of light responses ROM2F/2007/15, to appear Iodine 4 kev Iodine 40 kev No energy resolution Quenched peak with the straggling effect Dechanneled events Channeled events (q 1) Fraction of events with q ~ 1 (channeled events) Sodium 4 kev Sodium 40 kev NaI(Tl) (as those of DAMA) m W =20 GeV pure SI σ SI =10-6 pb halo model A5 NFW, v 0 =220 km/s, ρ max FF parameters and q factors at the mean values (case A in RNC26(2003)1) The effect of channeling on the energy spectra. An example: channeling differential rate, S 0 differential modulation amplitude, S m

28 What about the neutron calibrations of NaI(Tl) detectors? ROM2F/2007/15, to appear arxiv:physics/ (IDM 2006) Example of experimental data vs channeling modeling E det (kev) NIMA 507 (2003) 643 E det (kev) neutron data can contain channeled events but owing to the lowstatistics of these measurements and to the small effect looked for they cannot be identified At higher energy and for Iodine recoils the channeling effect becomes less important and gives more suppressed contributions in the neutron scattering data Detector responses to 10keV and 50keV Na recoils in NaI(Tl) taking into account the channeling effect.... broadened by energy resolution no energy res. with energy res. Therefore, there is no hope to identify the channeling effect in the already-collected neutron data on NaI(Tl)

29 ... while the accounting of the channeling effect can give a significant impact in the sensitivities of the Dark Matter direct detection methods when WIMP (or WIMP-like) candidates are considered. Effect for DM direct detection experiments Lower cross sections explorable for WIMP and WIMP-like candidates by crystal scintillators, such as NaI(Tl) (up to more than a factor 10 in some mass range), lower recoil energy thresholds, lower mass thresholds,... The same holds for purely ionization detectors, as Ge (HD-Moscow like). Loss of sensitivity when PSD is used in crystal scintillators (KIMS); in fact, the channeled events (q 1) are probably lost. No enhancement on liquid noble gas expts (DAMA/LXe, WARP, XENON10, ZEPLIN,...). No enhancement for bolometer double read-out expts; on the contrary some loss of sensitivity is expected since events (those with q ion 1) are lost by applying the discrimination procedures based on q ion «1.

30 Some examples of accounting for the channeling effect on the DAMA/NaI allowed regions ROM2F/2007/15, to appear the modeling in some given frameworks purely SI WIMP purely SD WIMP with without channeling for details on model frameworks see Riv.N.Cim 26 n1 (2003)1 SI & SD WIMP WARNING: to point out just the impact of the channeling effect the Migdal and SagDEG contributions have not been included here. the slices of the volumes shown here are focused just in the low mass region where the channeling effect is more effective

31 Other kind of interactions involved in the DM particle interactions on a detector?

32 Light bosons: Axion-like particles, similar phenomenology with ordinary matter as the axion, but significantly different values for mass and coupling constants are allowed. A wide literature is available and various candidate particles have been and can be considered. A complete data analysis of the total kgxday exposure from DAMA/NaI has been performed for pseudoscalar (a) and scalar (h) candidates in some of the possible scenarios. Allowed multi-dimensional volume Example of the pseudoscalar case (a)( Maximum allowed photon coupling only electron coupling cosmological interest: at least below Another class of DM candidates: light bosonic particles IJMPA21 (2006) 1445 The detection is based on the total conversion of the absorbed bosonic mass into electromagnetic radiation. Axion-like, some astrophysical hints: solar corona problem Di Lella & Zioutas X-ray from dark side of the Moon soft X-ray background radiation diffuse soft X-ray excess Hypothesis: ~ kev axion-like (K.K. axion) trapped in the Sun neighborhood and γγ decay In these processes the target nuclear recoil is negligible and not involved in the detection process (i.e. signals from these candidates are lost in experiments applying rejection procedures of the electromagnetic contribution) M a in proc e s s e s in v olv e d in th e de te c tion:,h,h h Di Lella, Zioutas AP19(2003)145 Majoron as in PLB99(1981)411 UHECR - PRD64(2001) The scalar case is interesting as well a h S 0 S 0,S m S 0,S m S 0 Many configurations are of cosmological interest S 0,S m S 0,S m

33 DAMA/NaI vs supersymmetric expectations in MSSM The result is consistent with the most popular candidate, the neutralino, over a large range of mass and cross sections (see the Scopel s talk) PRD69(2004) Assuming for the neutralino a dominant purely SI coupling when releasing the gaugino mass unification at GUT scale: M 1 /M (<); (where M 1 and M 2 U(1) and SU(2) gaugino masses) low mass configurations are obtained scatter plot of theoretical configurations vs DAMA/NaI allowed region in the given model frameworks for the total DAMA/NaI exposure (area inside the green line)... other DM candidate particles, as (see literature) the sneutrino in the Smith and Weiner scenario + a heavy ν of the 4-th family compatibility self-interacting dark matter mirror dark matter Kaluza-Klein particles (LKK) and more; even a suitable particle not yet foreseen by theories... indirect searches of DM particles in the space... and more heavy exotic canditates, as 4th family atoms,... light bosons PLB536(2002)263 Positron excess (see e.g. HEAT) Excess of Diffuse Galactic Gamma Rays for energies above 1 GeV in the galactic disk and for all sky directions (see EGRET). interpretation, evidence itself, derived m W and cross sections depend e.g. on bckg modeling, on DM spatial velocity distribution in the galactic halo, etc. Hints from indirect searches are not in conflict with DAMA/NaI for the WIMP class candidate

34 FAQ:... DAMA/NaI excluded by others? Obviously No They give a single model dependent result DAMA/NaI gives a model independent result No direct model independent comparison possible Assuming their expt. results as they quote: Case of DM particle scatterings on target-nuclei In general: The results are fully decoupled either because of the different sensitivities to the various kinds of candidates, interactions and particle mass, or simply taking into account the large uncertainties in the astrophysical (realistic and consistent halo models, presence of nonthermalized components, particle velocity distribution, particle density in the halo,...), nuclear (scaling laws, FFs, SF) and particle physics assumptions and in all the instrumental quantities (quenching factors, energy resolution, efficiency,...) and theor. parameters. At least in the purely SI coupling they only consider: OBVIOUSLY NO OBVIOUSLY NO Still room for compatibility either at low DM particle mass or simply accounting for the large uncertainties in the astrophysical, nuclear and particle physics assumptions and in all the expt. and theor. parameters. Case of bosonic candidate (full conversion into electromagnetic radiation) and of whatever e.m. component These candidates are lost by these expts. + they usually quote in an uncorrect, partial and unupdated way the implications of the DAMA/NaI model independent result OBVIOUSLY NO

35 The new DAMA/LIBRA set-up ~250 kg NaI(Tl) (Large sodium Iodide Bulk for RAre processes) As a result of a second generation R&D for more radiopure NaI(Tl) by exploiting new chemical/physical radiopurification techniques (all operations involving crystals and PMTs - including photos - in HP Nitrogen atmosphere) installing DAMA/LIBRA detectors assembling a DAMA/ LIBRA detector detectors during installation; in the central and right up detectors the new shaped Cu shield surrounding light guides (acting also as optical windows) and PMTs was not yet applied filling the inner Cu box with DAMA/LIBRA started operations on March 2003 further shield closing the Cu box housing the detectors view at end of detectors installation in the Cu box

36 DAMA/LIBRA Data collected up to March 2007: exposure: of order of 1.5 x 10 5 kg x d calibrations: acquired 40 M events of sources acceptance window eff: acquired 2 M ev/kev continuously running Stability of the low energy Stability of the high calibration factors energy calibration factors Examples: here from March 2003 to August 2005 frequency First σ=0.4% release of results σ=0.9% not later than end of 2008 frequency tdcal tdcal tdcal Model independent analysis already concluded almost in all the aspects on an exposure of + in progress f HE 0.40 ton year [(α β 2 ) = 0.537] f HE f HE all operations involving crystals and PMTs -including photosin HP N 2 atmosphere

37 Towards possible DAMA/1ton: now at R&D stage 1) Proposed since 1996 (DAMA/NaI and DAMA/LIBRA intermediate steps) 2) Technology largely at hand (large experiences and fruitful collaborations among INFN and companies/industries) 3) Still room for further improvements in the low-background characteristics of the set-up (NaI(Tl) crystals, PMTs, shields, etc.) 4) 1 ton detector: the cheapest, the highest duty cycle, the clear signature, the fast realization in few years A possible design: DAMA/1 ton can be realized by four replicas of DAMA/LIBRA: the detectors could be of similar size than those already used the features of low-radioactivity of the set-up and of all the used materials would be assured by many years of experience in the field electronic chain and controls would profit by the previous experience and by the use of compact devices already developped, tested and used. new digitizers will offer high expandibility and high performances the daq can be a replica of that of DAMA/LIBRA Electronic chain and example of the trigger system R&Ds on PMTs and crystals in progress 1 st detector prototype ready for measurements

38 KIMS: Some scintillation detector experiments either in preparation or at R&D stage Experimental site: Yangyang und. lab. (depth 700m) Detector: 4 CsI(Tl) scintillators of 8.7 kg mantained at 0 C Exposure: 3409 kg x day (arxiv: v2) Extracted Nuclear Recoils event rates of the CsI(Tl) crystals PSD to discriminate γ,e - / nuclear recoils ANAIS: NaI(Tl) scintillator for studying annual modulation signature in Canfranc laboratory Home-made efforts to improve old detectors. Example of a prototype: Energy spectra after data handling and cuts: about 10 cpd/kg/kev at 3 kev. Level of background still high. Cesium presence.

39 PICASSO 3 kg Some alternative techniques for direct detection experiments fluorine loaded active superheated liquid C 4 F 10 dispersed in the form of µm diameter droplets in a polymerized or viscous medium 32 detectors, 3 kg of C 4 F acoustic channels First detectors installed at SNOLAB Data taking ongoing SIMPLE: a freon-loaded superheated droplet detector (CF 3 I) the superheated droplet detectors COUPP (NUMI TUNNEL) MIMAC: MIcro-tpc Matrix of Chambers of He3 First results from a prototype submitted on april kg CF 3 I Bubble chamber until Sept. 06 running sensitive to SD and SI interactions also DMTPC, see Dujmic

40 Conclusions Different techniques can give complementary results Some further efforts to demonstrate the solidity of some techniques are desirable The model independent signature is the definite strategy to investigate the Dark Matter particles Solid experimental results obtained by considering different detectors, target materials, techniques, etc., can at least at some extent constrain the dark matter particle nature and disentangle among the different astrophysical scenarios, nuclear and particle physics models Felix qui potuit rerum cognoscere causas (Virgilio, Georgiche, li, 489)